Gaze tracking using optical coherence tomography

Abstract

Apparatus for gaze tracking an eye utilizing short coherence length interferometry, also known as optical coherence tomography ("OCT"). An embodiment of the present invention is an apparatus for gaze tracking an eye which includes: (a) an optical coherence tomography (OCT) apparatus; (b) a scanning apparatus for scanning across a predetermined portion of the eye with optical output from the OCT apparatus; (c) an analysis apparatus for analyzing detection signals output from the OCT apparatus to determine a location of a feature of the eye; (d) an illumination apparatus for producing a reflection of radiation from a cornea of the eye (corneal reflex); (e) a detection apparatus for determining a location of the corneal reflex; and (f) the analysis apparatus further includes an apparatus which is responsive to the location of the feature and to the location of the corneal reflex for gaze tracking.

What is claimed is: 
     
       1. Apparatus for gaze tracking an eye which comprises: an optical coherence tomography (OCT) apparatus that generates optical output and generates detection signals in response to backscattered optical output;   a scanner that scans the optical output along one or more trajectories across a predetermined portion of the eye and transfers to the OCT apparatus portions of optical output backscattered from materials in the eye;   a depth analyzer that analyzes the detection signals at various positions along the one or more trajectories to determine depths in the eye of the materials that backscattered the optical output:   a location analyzer, responsive to the depths, that determines a location of a feature of the eye;   an illuminator which produces a reflection of radiation from a cornea of the eye (corneal reflex);   a detector which determines a location of the corneal reflex; and   a gaze tracker, responsive to the location of the feature and to the location of the corneal reflex, which tracks the gaze.   
     
     
       2. The apparatus of claim 1 wherein the feature is a pupil and the location of the feature is a center of the pupil. 
     
     
       3. The apparatus of claim 2 wherein the location analyzer further determines: sin θ x  =(x cr  -x p )/(A-a) and sin θ y  =(y cr  -y p )/(A-a) where (θ x , θ y ) are measures of change in gaze direction in x and y, respectively, (x cr  -x p ) and (y cr  -y p ) are distances in x and y, respectively, between the center of the corneal reflex and the center of the pupil; A is a calibrated distance from a center of rotation of the eye to an outer corneal surface and a is calibrated radius of curvature of the outer surface of the cornea.   
     
     
       4. The apparatus of claim 1 wherein the location analyzer determines locations at which depth in the eye of material at positions along a trajectory are different by a predetermined amount from depth in the eye of material at other positions along the trajectory. 
     
     
       5. The apparatus of claim 4 wherein the predetermined portion of the eye includes a pupil/iris boundary. 
     
     
       6. The apparatus of claim 4 wherein: the scanner scans the optical output along trajectories that cross a pupil/iris boundary at least three times; and   the location analyzer determines at least three locations on the pupil/iris boundary.   
     
     
       7. The apparatus of claim 6 wherein the location analyzer further comprises a center finder which determines a center of the pupil from the locations on the pupil/iris boundary. 
     
     
       8. The apparatus of claim 4 wherein the location analyzer determines locations at which amplitude of the detection signals exceed a predetermined amount. 
     
     
       9. Apparatus for gaze tracking an eye which comprises: on optical coherence tomography (OCT) apparatus that generates optical output and generates detection signals in response to backscattered optical output;   a scanner, in response to coarse scan commands from a controller, that coarse scans the optical output over a two-dimensional grid which encompasses at least a portion of a pupil/iris boundary and transfers to the OCT apparatus portions of optical output backscattered from materials in the eye;   a depth analyzer that analyzes detection signals from the coarse scan at various positions over the grid to determine depths in the eye of the materials that backscattered the optical output;   a location analyzer, responsive to the depths from the coarse scan, that determines a coarse pupil/iris boundary;   wherein the scanner, in response to fine scan commands from the controller, fine scans the optical output along one or more trajectories across the coarse pupil/iris boundary and transfers to the OCT apparatus portions of optical output backscattered from materials in the eye;   wherein the depth analyzer analyzes detection signals from the fine scan at various positions along the one or more trajectories to determine depths in the eye of the materials that backscattered the optical output; and   wherein the location analyzer, responsive to the depths from the fine scan, determines the center of the pupil.   
     
     
       10. Apparatus for gaze tracking an eye which comprises: an optical coherence tomography (OCT) apparatus that generates optical output and generates detection signals in response to backscattered optical output;   a scanner that scans the optical output along one or more trajectories across a predetermined portion of the eye and transfers to the OCT apparatus portions of optical output backscattered from materials in the eye;   a depth analyzer that analyzes the detection signals at various positions along the one or more trajectories to determine depths in the eye of the materials that backscattered the optical output:   a location analyzer, responsive to the depths, that determines a location of a feature on a fundus of the eye; and   a gaze tracker, responsive to the location of the feature, that tracks the gaze.   
     
     
       11. The apparatus of claim 10 wherein the location analyzer determines locations at which depth in the eye of material at positions along a trajectory are different by a predetermined amount from depth in the eye of material at other positions along the trajectory. 
     
     
       12. The apparatus of claim 11 wherein the location analyzer further determines sin θ32 D/R where θ is a measure of change of gaze direction, D is a calibrated distance the feature moves, and R is a radius of the eyeball. 
     
     
       13. The apparatus of claim 11 wherein the feature is one of a foveola and a papilla. 
     
     
       14. The apparatus of claim 11 wherein the feature is a pattern of blood vessels. 
     
     
       15. Apparatus for gaze tracking an eye which comprises: an optical coherence tomography (OCT) apparatus that generates optical output and generates detection signals in response to backscattered optical output:   a scanner that scans the optical output over a two-dimensional grid which encompasses a feature, the grid having a spacing which is smaller than a size of the feature and transfers to the OCT apparatus portions of optical output backscattered from materials in the eye;   a depth analyzer that analyzes detection signals from the scan at various positions over the grid to determine depths in the eye of materials that backscattered the optical output;   a location analyzer, responsive to the depths from the scan, that determines a location of the feature.   
     
     
       16. A method for gaze tracking an eye which comprises the steps of: scanning radiation output from an optical coherence tomography (OCT) apparatus along one or more trajectories across a predetermined portion of the eye and transferring to the OCT apparatus portions of optical output backscattered from materials in the eye;   analyzing detection signals output from the OCT apparatus in response to the backscattered optical output at various positions along the one or more trajectories to determine depths in the eye of materials that backscattered the optical output:   determining a location of a feature of the eye from the depths;   illuminating the eye to produce a reflection of radiation from a cornea of the eye (corneal reflex);   detecting a location of the corneal reflex; and   gaze tracking in response to the location of the feature and to the location of the corneal reflex.   
     
     
       17. Apparatus for gaze tracking an eye which comprises: an optical coherence tomography (OCT) apparatus that generates optical output and generates detection signals in response to backscattered optical output;   a scanning means for scanning the optical output along one or more trajectories across a predetermined portion of the eye and for transferring to the OCT apparatus portions of optical output backscattered from materials in the eye;   a depth analyzer means for analyzing the detection signals at various positions along the one or more trajectories to determine depths in the eye of materials that backscattered the optical output;   a location analyzer means, responsive to the depths, for determining a location of a feature of the eye;   illumination means for producing a reflection of radiation from a cornea of the eye (corneal reflex);   detecting means for determining a location of the corneal reflex; and   a gaze tracker means, responsive to the location of the feature and to the location of the corneal reflex, for gaze tracking.   
     
     
       18. The apparatus of claim 17 wherein the feature is a feature on the fundus. 
     
     
       19. Apparatus for gaze tracking an eye which comprises: an optical coherence tomography (OCT) apparatus that generates optical output and generates detection signals in response to backscattered optical output;   a scanner means, in response to commands from a controller, for scanning the optical output over a two-dimensional grid that encompasses a feature and for transferring to the OCT apparatus portions of the optical output backscattered from materials in the eye;   a depth analyzer means for analyzing the detection signals at various positions over the grid to determine depths in the eye of materials that backscattered the optical output; and   a location analyzer means, responsive to the depths, for determining a location of the feature.   
     
     
       20. The apparatus of claim 19 wherein: location analyzer means comprises boundary means for determining a coarse feature boundary;   wherein the scanning means, responsive to fine scan commands from the controller, comprises means for scanning the optical output along one or more trajectories across the coarse feature boundary and for transferring to the OCT apparatus portions of the optical output backscattered from materials in the eye;   wherein the depth analyzer means further comprises fine depth analyzer means, for analyzing detection signals from the fine scan at various positions along the one or more transverse trajectories to determine depths in the eye of materials that backscattered the optical output; and;   wherein the location analyzer means further comprises means, responsive to the depths from the fine scan, for determining the location of the feature.